Methylene blue photoelectrodegradation under UV irradiation on Au/Pd-modified TiO2 films

In this work TiO₂ thin films were modified with gold/palladium (Au/Pd) bimetallic paticles by sputtering method. TiO₂ films were deposited on ITO (SnO₂:In) by Doctor Blade method and post-anneling. The properties of the films were studied through measurements of XRD (X-ray diffraction) and AFM (atomic force microscopy). The degradation of methylene blue was studied by UV-irradiated pure TiO₂ and Au/Pd-modified TiO₂ in aqueous solution. Langmuir-Hinshelwood model was used to obtain kinetic information. Photocatalytic study indicated that Au/Pd-modified TiO₂ photocatalytic activity was better than TiO₂ pure; the best half-life time for Au/Pd-modified TiO₂ in photodegradation was 2.8 times smaller than TiO₂ pure; finally the efficiency in methylene blue photodegradation was improved from 23% to 43% when Au/Pd-modified TiO₂ films were used.     

Preparation, characterization of Au (or Pt)-loaded titania nanotubes and their photocatalytic activities for degradation of methyl orange

TiO₂ nanotubes were prepared by hydrothermal method and Au (or Pt) was loaded on TiO₂ nanotubes by photodeposition method. The photocatalysts were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and N₂ adsorption technique, respectively. The photocatalytic properties of the samples were also investigated. The results show that TiO₂ nanotubes with uniform diameter were prepared, and they have specific surface areas over 400 m²/g. The specific surface areas of TiO₂ nanotubes decrease with the increasing of calcining temperature, and crystalline phase of TiO₂ in the wall of nanotubes was transformed from anatase into rutile phase in calcination process. The photocatalytic activities of TiO₂ nanotubes are higher than that of nanosized TiO₂, and the photocatalytic activities of TiO₂ nanotubes were enhanced after loading Au (or Pt). After irradiation for 40 min under a 300 W of middle-pressure mercury lamp (MPML), the degradation rate of methyl orange solution using the Au/TiNT-500 (or Pt/TiNT-500) as a catalyst can reach 96.1% (or 95.1%). On the other hand, Au-loaded sample has evident adsorption peak in visible range, indicating that Au-loaded TiO₂ nanotubes are hopeful to become visible light photocatalyst.     

The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering

This paper seeks to determine the optimal settings for the deposition parameters, for TiO₂ thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO₂ target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (°C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO₂. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (1 1 0) and (2 0 0) peaks of the rutile structure and the (2 0 0) peak of the anatase structure were observed, at 2θ ∼ 27.4°, 39.2° and 48°, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO₂ film, because of the increased strength of the interface of micro-blasted tools.     

Photodegradation of CH3I on mesoporous TiO2-B nanofibers with Au nanoparticles

Au nanoparticles deposited on mesoporous TiO₂-B nanofibers have been prepared, characterized, and used to catalyze photoreactions of iodomethane. High-density gold-particle deposition on TiO₂-B is obtained by electrostatic and/or chemical force between the particles of TiO₂-B and Au capped with -SC(H)(CO₂H)(CH₂CO₂H) through pH control. The capping groups on the gold particles can be removed after 400 °C calcination. It is found that the nature of the inorganic acids used for pH adjustment has effects on particle morphology and deposition. Two other methods, i.e., preparation of TiO₂-B nanofibers in the presence of gold particles and preparation of gold nanoparticles in the presence of TiO₂-B particles (deposition-precipitation method), are also investigated. However, the former method produces a low-density deposition and the latter one induces a morphology change of the TiO₂-B and an increase of the Au in size. Fourier transform infrared spectroscopy has been employed to study and to compare the photoreactions of CH₃I on TiO₂-B and Au/TiO₂-B and the effect of O₂. The presence of gold particles on TiO₂-B increases the efficiency of CH₃I photodegradation, forming adsorbed methoxy and formate. The role of gold is also discussed.     

亚纳米厚的氧化铝包裹层可以显著提高负载型金纳米颗粒催化剂的热稳定性

负载型金纳米颗粒催化剂在许多催化反应中展现出非常好的催化活性,但是金纳米颗粒在高温等反应条件下容易烧结团聚,极大地限制了金催化剂的应用。利用原子层沉积技术在Au/TiO₂催化剂表面分别精确沉积了一层超薄的二氧化钛和氧化铝包裹层,并对比研究了包裹层对金纳米颗粒的热稳定性影响。原位红外漫反射CO吸附和x-射线光电子能谱数据证实了氧化物包裹层的存在。发现亚纳米厚的氧化铝包裹层能够在600 C完全避免金纳米颗粒的团聚;相反,二氧化钛包裹层对金纳米颗粒稳定性的提高没有明显效果。通过CO氧化探针反应的活性测试,发现随着煅烧温度的升高氧化铝包裹的Au/TiO₂ 催化剂的活性逐渐提高,表明高温处理可以促进被包裹金原子的暴露并表现出催化活性。提供了提高金纳米颗粒稳定性的有效方法,为拓展金催化剂在条件苛刻的反应中的应用奠定了技术基础.     

Influence of Au thickness on the optical and electrical properties of transparent and conducting TiO2/Au/TiO2 multilayer films

Au-intermediate TiO₂/Au/TiO₂ (TAT) multilayer films were deposited by RF magnetron sputtering onto glass substrates. Changes in the optical and electrical properties of the films were investigated with respect to the thickness of the Au interlayer.The observed optical and electrical properties were dependent on the thickness of the Au interlayer. The resistivity decreased to 3.3 × 10⁻⁴ Ω cm for TiO₂ films with a 20 nm-thick Au interlayer and the optical transmittance was also influenced by the Au interlayer. Although optical transmittance deteriorated as Au thickness increased, TiO₂ films with a 5 nm-thick Au interlayer showed a relatively high optical transmittance of 80% at a wavelength of 550 nm. In addition, since a TAT film with a 5 nm-thick Au interlayer showed a relatively high work function value, it is an alternative candidate for use as a transparent anode in OLEDs and flat panel displays.     

Influence of deposition atmosphere on photocatalytic activity of TiO2/SiOx double-layers prepared by RF magnetron sputtering

TiO₂/SiO_x double-layers have been prepared at room temperature by RF magnetron sputtering. The TiO₂ top-layer was deposited in an Ar atmosphere, while the SiO_x bottom-layer was deposited in an Ar/O₂ atmosphere. Samples were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and photoluminescence techniques. The photocatalytic activity of the samples was evaluated by the photodegradation of methylene blue; the results showed that the photocatalytic activity of the TiO₂/SiO_x double-layers was superior to that of the TiO₂ single-layers. The presence of the SiO_x bottom-layer improved the photocatalytic activity of the TiO₂ layer because it may act as a trap for electrons generated in the TiO₂ layer thus preventing electron-hole recombinations.     

A versatile sonication-assisted deposition–reduction method for preparing supported metal catalysts for catalytic applications

This work aims to develop a rapid and efficient strategy for preparing supported metal catalysts for catalytic applications. The sonication-assisted reduction–precipitation method was employed to prepare the heterogeneous mono- and bi-metallic catalysts for photocatalytic degradation of methyl orange (MO) and preferential oxidation (PROX) of CO in H₂-rich gas. In general, there are three advantages for the sonication-assisted method as compared with the conventional methods, including high dispersion of metal nanoparticles on the catalyst support, the much higher deposition efficiency (DE) than those of the deposition–precipitation (DP) and co-precipitation (CP) methods, and the very fast preparation, which only lasts 10–20 s for the deposition. In the AuPd/TiO₂ catalysts series, the AuPd(3:1)/TiO₂ catalyst is the most active for MO photocatalytic degradation; while for PROX reaction, Ru/TiO₂, Au–Cu/SBA-15 and Pt/γ-Al₂O₃ catalysts are very active, and the last one showed high stability in the lifetime test. The structural characterization revealed that in the AuPd(3:1)/TiO₂ catalyst, Au–Pd alloy particles were formed and a high percentage of Au atoms was located at the surface. Therefore, this sonication-assisted method is efficient and rapid in the preparation of supported metal catalysts with obvious structural characteristics for various catalytic applications.     

Photocatalytic degradation of BTEX using W-doped TiO2 immobilized on fiberglass cloth under visible light

W-doped TiO₂ were immobilized on fiberglass cloth (FGC). The catalyst possessed small crystallite sizes with a red-shift on an absorption edge. Good dispersion was observed over the immobilized catalyst. The photocatalytic degradation of gaseous BTEX was conducted in a flow reactor under day-light fluorescent. Parameters including gas flowrate, catalyst loading, initial concentration and relative humidity (%RH) were investigated. The prepared catalysts showed higher efficiency than that of TiO₂ approximately 18, 3, 3 and 2.5× for benzene, toluene, ethylbenzene and o-xylene, respectively. The condition to achieve 100% BTEX removal was found at 20 min/ml, catalyst loading 0.1 mg/cm² and 30% RH.     

Investigation into the effects of deposition parameters on TiO2 photocatalyst thin films by rf magnetron sputtering

Titanium dioxide (TiO₂) photocatalyst thin films were deposited on non-alkali glass substrates by radio frequency (rf) magnetron sputtering. The Taguchi method with orthogonal array, signal-to-noise ratio and analysis of variance were employed to study the performance characteristics. The experimental studies were conducted under different rf powers, sputtering pressures, O₂/(Ar+O₂) flow-rate ratios, and substrate temperatures. The deposited TiO₂ films were of the anatase phase with a (101) preferred orientation. We performed both photoinduced decomposition of methylene blue (MB) and photoinduced hydrophilicity under UV light illumination. With the optimized TiO₂ photocatalyst thin film deposition conditions, the water contact angle after 9 min UV illumination was approximately 5, the absorbance of MB was reduced to 0.2 for 240 min UV irradiation, and the deposition rate was 34.18 Å/min.     

A novel approach towards high-performance composite photocatalyst of TiO2 deposited on activated carbon

TiO₂ photocatalysts deposited on activated carbon (TiO₂/AC) were prepared by dip-hydrothermal method at 180 °C using peroxotitanate as a precursor, then calcinated at 300-800 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and the nitrogen absorption. Their photocatalytic activity was evaluated by degradation of methyl orange (MO). The results showed that TiO₂ particles of anatase type were well deposited on the activated carbon surface. TiO₂/AC calcinated at 600 °C exhibited the best photocatalytic performance. For the comparison, the same photocatalysis experiment was carried out for two mixtures of commercial TiO₂ (Degussa P25) with AC and synthetic TiO₂ with AC. It was found that the composite catalyst TiO₂/AC was better than the two mixtures. Besides, different from fine powdered TiO₂, the granular TiO₂/AC photocatalysts could be easily separated from the bulk solution and reused; indeed, its photocatalytic ability was hardly decreased after a five-cycle for MO degradation. The kinetics of the MO degradation fitted well the Langmuir-Hinshelwood model.     

Reasons for the deactivation of Pt/TiO2 photocatalyst treated by inert gas N2

The effect of N₂ treatment on the photocatalytic activity of Pt⁰/TiO₂ was investigated. The results showed that after treatment at 500 °C in N₂, 70% of the photocatalytic activity of 1.0 wt.% Pt⁰/TiO₂ was lost by the evaluation of photocatalytic oxidation reaction of C₃H₆. Transmission electron microscopy (TEM) and Ar⁺ ion sputtering tests revealed that in the course of high-temperature N₂ treatment, the size of Pt⁰ particles on TiO₂ increases and a strong interaction between metal and support, i.e. Pt⁰ particles encapsulated by Ti_xO_y, happens, which are the reasons for the deactivation of Pt⁰/TiO₂ photocatalyst treated by high-temperature N₂.     

Characterization of TiO2/Au/TiO2 films deposited by magnetron sputtering on polycarbonate substrates

Transparent and conducting TiO₂/Au/TiO₂ (TAuT) films were deposited by reactive magnetron sputtering on polycarbonate substrates to investigate the effect of the Au interlayer on the optical, electrical, and structural properties of the films. In TAuT films, the Au interlayer thickness was kept at 5 nm. Although total thickness was maintained at 100 nm, the stack structure was varied as 50/5/45, 70/5/25, and 90/5/5 nm.In XRD pattern, the intermediate Au films were crystallized, while all TAuT films did not show any diffraction peaks for TiO₂ films with regardless of stack structure. The optical and electrical properties were dependent on the stack structure of the films. The lowest sheet resistance of 23 Ω/□ and highest optical transmittance of 76% at 550 nm were obtained from TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films. The work function was dependent on the film stack. The highest work function (4.8 eV) was observed with the TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm film stack. The TAuT film stack of TiO₂ 90 nm/Au 5 nm/TiO₂ 5 nm films is an optimized stack that may be an alternative candidate for transparent electrodes in flat panel displays.     

二氧化钛修饰的微结构聚合物光纤预制棒制备及其在光催化中应用的探索研究

首次用二氧化钛(TiO₂)纳米材料修饰的547孔微结构聚合物光纤(MPOF)二次预制棒作为阵列化微管式光催化反应器对亚甲基兰的光催化分解进行研究.将高光催化活性的P25型二氧化钛纳米粒子均匀分散在TiO₂溶胶中,对547孔微结构聚合物光纤孔洞内壁进行铺膜,得到了负载光催化剂的阵列化微管材料.该TiO₂MPOF有序复合的阵列化微管不仅对二氧化钛纳米粒子起到负载作用,还可以作为光波导介质(rolling-up薄膜波导,聚光、导光进入二氧化钛薄膜层)、污染物反应流体通道.以有机染料亚甲基兰为模拟污染物,研究了TiO₂负载量、亚甲基兰的初始浓度及溶液pH值等因素对光降解效果的影响.该反应器547个孔道的内表面用于负载光催化剂,不仅增加了固-液接触面积,也提高了光的吸收效率,从而提高了光催化效率.迄今为止,这种兼具导光、聚光、传质、负载功能于一体的光催化反应器还未见报道.     

Characterization and photocatalytic activity of Zn–TiO2/AC composite photocatalyst

Activated carbon (AC) supported Zn²⁺–TiO₂ photocatalyst was prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction, scanning electron micrograph, nitrogen absorption, diffuse reflectance UV/VIS and X-ray photoelectron spectroscopy. Using toluene as a pollution target, the photocatalytic activity of photocatalyst was evaluated. The results showed that prepared photocatalyst was obviously helpful for the removal of toluene in air. The photocatalytic degradation of toluene by Zn²⁺–TiO₂/AC reached 100% for 40 min and remained 75% after 160 min, while degradation by TiO₂ was only 30%. It indicated that the photocatalytic activity of prepared photocatalyst was enhanced. It is due to Zn²⁺-doping increased the oxidation and reduction of hole–electron pairs, which was the important factor in heterogeneous photocatalysis.     

Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO₂–SiO₂ thin film was prepared by self-assembly method by mixing SiO₂ precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO₂ and even anatase TiO₂ but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO₂ was incorporated into the film. The self-assembly TiO₂–SiO₂ thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO₂ are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO₂:TiO₂) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.     

Highly Active TiO2/Polyelectrolytes Hybrid Multilayered Hollow Nanofibrous Photocatalyst Prepared from Electrouspun Fibers Using Electrostatic Layer-by-Layer Technique

Compared to conventional film photocatalysts, fiber photocatalyst has a greater surface-to-volume ratio and a 3-D open structure that allows its surface active sites to be accessible for reactants more easily and effectively. However, TiO ₂ powder (Degussa P25), by itself, cannot be prepared in the form of fibers, but with the help of a polymer nanofiber, TiO ₂ particles can be immobilized in a fibrous network of polyelectrolyte. Here, hybrid multilayered hollow nanofibers (HMHNFs) composed of TiO ₂ /polyelectrolyte (PE) have been prepared by a combination of a electrospinning method and layer-by-layer (LBL) technology. The results show that both the average diameter and the wall thickness of the HMHNFs can be well controlled by the template, as well as the number of coating layers. The dried morphology of the obtained HMHNFs is dependent on the inner deposited numbers of the polyelectrolyte layers. When compared with other nanostructured TiO ₂ materials, such as commercial TiO ₂ nanoparticles (P25, Degussa) and TiO ₂ films, the hollow TiO ₂ /PE hybrid nanofibers exhibited higher photocatalytic activities.     

Enhanced optical properties of Al-doped TiO2 thin films in oxygen or nitrogen atmosphere

Al-doped TiO₂ (TiO₂:Al) films were deposited by simultaneous RF magnetron sputtering of TiO₂ and DC magnetron sputtering of Al. The advantage of this method is that the Al content could be independently controlled. By depositing in a mixed Ar-O₂ or a mixed Ar-N₂ atmosphere, the TiO₂:Al film became more stoichiometric and the nanocrystallinity was enhanced. The nonlinear refractive index of TiO₂:Al film deposited in a pure Ar, a mixed Ar-O₂ or a mixed Ar-N₂ atmosphere was measured by Moiré deflectometry, and was of the order of 10⁻⁸ cm² W⁻¹. For the TiO₂:Al film deposited in a pure Ar atmosphere, the porosity was higher corresponding to the lower transmission. However, the porosity of TiO₂:Al film decreased as the oxygen or nitrogen pressure increased. Especially, as the ratio of O₂ to Ar pressure increased to 0.22, TiO₂:Al film exhibited lower porosity, higher visible transmission, higher linear refractive index, lower stress and lower stress-optical coefficient.     

Synthesis, characterization and effect of calcination temperature on phase transformation and photocatalytic activity of Cu,S-codoped TiO2 nanoparticles

A novel copper and sulfur codoped TiO₂ photocatalyst was synthesized by modified sol-gel method using titanium(IV) isopropoxide, CuCl₂·2H₂O and thiourea as precursors. The samples were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy equipped with energy dispersive X-ray micro-analysis (SEM-EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) analysis. The XRD results showed undoped and Cu,S-codoped TiO₂ nanoparticles only include anatase phase. Effect of calcination temperature showed rutile phase appears in 650 and 700 °C for undoped and 0.1% Cu,S-codoped TiO₂, respectively. The SEM analysis revealed the doping of Cu and S does not leave any change in morphology of the catalyst surface. The increase of copper doping enhanced “red-shift” in the UV-vis absorption spectra. The TEM images confirmed the dopants suppressed the growth of TiO₂ grains. The photocatalytic activity of samples was tested for degradation of methyl orange (MO) solutions. The results showed photocatalytic activity of the catalysts with 0.05% Cu,0.05% S and 0.1% Cu,0.05% S were higher than that of other catalysts under ultraviolet (UV) and visible irradiation, respectively. Because of synergetic effect of S and Cu, the Cu,S-codoped TiO₂ catalyst has higher activity than undoped and Cu or S doped TiO₂ catalysts.